The common carp is a well-known, fairly large Eurasian fish that tolerates poor water quality, feeds on organic material in mud, and reproduces prolifically. It seems like a natural choice for artificial introduction, to provide a sustainable food source in an urban environment. Unfortunately, in the United States, the sport of carp-fishing is not popular, and the meat of this fish is not much sought after. Those few who do fish for urban carp are warned that these animals may have high levels of carcinogenic pcbs in their tissues. In the absence of human predation, urban waterways have become havens for common carp. Their bottom-feeding habits stir sediments into the water, making their habitat unsuitable for other fish that require cleaner water, or higher oxygen levels.

In some urban areas, such as Boston's Jamaica Pond, there are introduced Japanese Koi, which are common carp that have been bred in captivity for their bright orange and white colors. A 20 pound koi was caught there in 2005. Goldfish are carp relatives, and the same hobby of captive breeding produced the baffling variety of goldfish as well as koi.

Mature common carp are so large that they have no urban predators. The largest carp recorded have been over three feet and over eighty pounds. They can be fascinating to watch from urban bridges as they glide below the surface, or burst out of it, displaying their spawning behavior.